1. Field of the Invention
The present invention relates to a method of controlling nozzles of an inkjet head, and more particularly, to an apparatus for measuring the amounts of ink ejected from nozzles of an inkjet head.
2. Description of the Related Art
In general, inkjet heads are devices that eject ink droplets onto desired positions of a recording medium through nozzles to form an image. Inkjet heads have recently been applied to various electronic devices such as liquid crystal displays (LCDs), organic light emitting displays (OLEDs), and organic thin film transistors (OTFTs).
FIG. 1 is a cross-sectional view for explaining a method of manufacturing a color filter for an LCD by using an inkjet head 50. Referring to FIG. 1, ink droplets 60 of predetermined colors are ejected through nozzles 55 of the inkjet head 50 and filled in pixels disposed on a substrate 10. Next, the ink is dried to form solid ink layers 65 in the pixels 22 to predetermined thicknesses. A black matrix 20 is formed on the substrate 20 and defines the pixels 22. In the manufacture of the color filter, the nozzles 55 of the inkjet head 50 may have different ejection characteristics such that different amounts of ink may be ejected through the nozzles 55. Accordingly, the ink layers 65 may be formed to different thicknesses in the pixels 22 as shown in FIG. 2, thereby causing significant degradation of color quality.
In order to uniformize the thicknesses of the ink layers 65, the same amount of ink should be ejected through all the nozzles 55 of the inkjet head 50 during a printing operation. To this end, it is necessary to control waveforms of voltages applied to the nozzles 55 of the inkjet head 50. Thus, various methods of controlling nozzles of an inkjet head have been suggested. For example, the masses of ink droplets ejected through the nozzles may be measured using a scale, such as a load cell. Alternatively, the volumes of ink droplets ejected through the nozzles may be measured using a camera. Alternatively, after ink droplets ejected through the nozzles are filled in pixels and dried, the thicknesses of ink layers formed in the pixels may be measured. However, the method of measuring the masses of the ink droplets using the scale may generate measurement errors and is time consuming. Also, the method of measuring the volumes of the ink droplets is difficult when the ink droplets have irregular shapes. Furthermore, since the method of measuring the thicknesses of the ink layers filled in the pixels involves a drying process, it takes much time to measure the thicknesses of the ink layers.